1. Field of the Invention
The invention relates to a semiconductor device and a method of fabricating the same, and more particularly to a semiconductor device having a wiring structure which enhances a resistance to electromigration, and a method of fabricating the same.
2. Description of the Related Art
There have been suggested a lot of wiring structures for electrically connecting an upper wiring layer and a lower wiring layer to each other through a metal plug.
As a first example of a conventional wiring structure, the wiring structure suggested in Japanese Unexamined Patent Publication No. 5-326511 is illustrated in FIG. 1.
The illustrated wiring structure is comprised of a silicon substrate 51, a first electrically insulating film 52 composed of silicon dioxide and formed on the silicon substrate 51, a titanium film 53 formed on the first electrically insulating film 52, a first titanium nitride film 54 formed on the titanium film 53, a first aluminum-copper alloy film 55 formed as a lower wiring layer on the first titanium nitride film 54, a second titanium nitride film 56 formed on the first aluminum-copper alloy film 55, a second electrically insulating film 57 composed of silicon dioxide and formed on the second titanium nitride film 56, a third titanium nitride film 58 covering an inner surface of a through-hole 57a formed throughout the second electrically insulating film 57, and a surface of the second electrically insulating film 57 therewith, and acting as a barrier metal for a later mentioned tungsten plug 59, a tungsten plug 59 filled in the through-hole 57a, and a second aluminum-copper alloy film 60 formed as an upper wiring layer on both the tungsten plug 59 and the third titanium nitride film 58.
The wiring structure illustrated in FIG. 1 is fabricated as follows.
First, there are formed the first electrically insulating film 52, the titanium film 53, the first titanium nitride film 54, the first aluminum-copper alloy film 55, the second titanium nitride film 56 and the second electrically insulating film 57 in this order on the silicon substrate 51. Then, the through-hole 57a is formed throughout the second electrically insulating film 57 such that the through-hole 57a reaches the first aluminum-copper alloy film 55.
Then, the third titanium nitride film 58 is formed on an inner surface of the through-hole 57a and a surface of the second electrically insulating film 57 by DC magnetron sputtering, for instance. The third titanium nitride film 58 acts as a barrier metal for the tungsten plug 59.
Then, the through-hole 57a is filled with tungsten. Then, the tungsten is etched back until the third titanium nitride film 58 appears.
Thereafter, the second aluminum-copper alloy film 60 is formed as an upper wiring layer on both the tungsten plug 59 and the third titanium nitride film 58.
FIG. 2 illustrates a second example of a conventional wiring structure for electrically connecting upper and lower wiring layers to each other through a metal plug.
The illustrated wiring structure is comprised of a silicon substrate 61, a first electrically insulating film 62 composed of silicon dioxide and formed on the silicon substrate 61, a first titanium film 63 formed on the first electrically insulating film 62, a first titanium nitride film 64 formed on the first titanium film 63, a first aluminum-copper alloy film formed as a lower wiring layer on the first titanium nitride film 64, a second titanium nitride film 66 formed on the first aluminum-copper alloy film 65, a second electrically insulating film 67 composed of silicon dioxide and formed on the second titanium nitride film 66, a third titanium nitride film 68 covering an inner surface of a through-hole 67a formed throughout the second electrically insulating film 67, and a surface of the second electrically insulating film 67 therewith, and acting as a barrier metal for a later mentioned tungsten plug 69, a tungsten plug 69 filled in the through-hole 67a, a second titanium film 70 covering the tungsten plug 69 and the second electrically insulating film 67 therewith, a fourth titanium nitride film 71 formed on the second titanium film 70, and a second aluminum-copper alloy film 72 formed as an upper wiring layer on the fourth titanium nitride film 71.
The wiring structure illustrated in FIG. 2 is fabricated as follows.
First, there are formed the first electrically insulating film 62, the first titanium film 63, the first titanium nitride film 64, the first aluminum-copper alloy film 65, the second titanium nitride film 66 and the second electrically insulating film 67 in this order on the silicon substrate 61. Then, the through-hole 67a is formed throughout the second electrically insulating film 67 such that the through-hole 67a reaches the first aluminum-copper alloy film 65.
Then, the third titanium nitride film 68 is formed on an inner surface of the through-hole 67a and a surface of the second electrically insulating film 67 by DC magnetron sputtering, for instance. The third titanium nitride film 68 acts as a barrier metal for the tungsten plug 69.
Then, the through-hole 67a is filled with tungsten. Then, the third titanium nitride film 68 formed on the second electrically insulating film 67 is removed by chemical mechanical polishing (CMP) until the second electrically insulating film 67 appears.
Thereafter, there are formed the second titanium film 70, the fourth titanium nitride film 71 and the second aluminum-copper alloy film 72 in this order over the tungsten plug 69 and the second electrically insulating film 67.
As a third example of a conventional wiring structure, the wiring structure suggested in Japanese Unexamined Patent Publication No. 11-354519 is illustrated in FIG. 3.
The illustrated wiring structure is comprised of a silicon substrate 71, a first electrically insulating film 72 formed on the silicon substrate 71, a first titanium film 73 covering therewith an inner surface of a through-hole 72a formed throughout the first electrically insulating film 72, a first titanium nitride film 74 entirely covering the first titanium film 73 therewith, a first tungsten plug 75 buried in the through-hole 72a, a second electrically insulating film 76 formed on the first electrically insulating film 72, a second titanium film 77 formed on the first electrically insulating film 72, entirely covering the first tungsten plug 75 therewith, a second titanium nitride film 78 formed on the second titanium film 77, a first aluminum-copper alloy film 79 formed as a lower wiring layer on the second titanium nitride film 78, a third titanium film 80 formed on the first aluminum-copper alloy film 79, a third titanium nitride film 81 formed on the third titanium film 80, a fourth titanium film 82 entirely covering an inner surface of a through-hole 76a formed throughout the second electrically insulating film 76, a fourth titanium nitride film 83 entirely covering the fourth titanium film 82 therewith, a second tungsten plug 84 buried in the through-hole 76a, a fifth titanium film 85 formed on the second electrically insulating film 76, entirely covering the second tungsten plug 84 therewith, a fifth titanium nitride film 86 formed on the fifth titanium film 85, a second aluminum-copper alloy film 87 formed as an upper wiring layer on the fifth titanium nitride film 86, a sixth titanium film 88 formed on the second aluminum-copper alloy film 87, and a sixth titanium nitride film 89 formed on the sixth titanium film 88.
In the wiring structure, the first titanium film 73 and the first titanium nitride film 74 act as a barrier metal for the first tungsten plug 75, and the fourth titanium film 82 and the fourth titanium nitride film 83 act as a barrier metal for the second tungsten plug 84.
In the wiring structure illustrated in FIG. 1 as a first example of a conventional wiring structure, the aluminum-copper alloy film 60 is formed as an upper wiring layer on the third titanium nitride film 58. Titanium nitride has <111> orientation, and aluminum-copper alloy has <111> orientation.
However, if the aluminum-copper alloy film 60 having <111> orientation is formed on the second electrically insulating film 57 with the titanium nitride film 58 having <111> orientation which is closer to the orientation of aluminum-copper alloy, being sandwiched therebetween, <111> orientation of aluminum in the aluminum-copper alloy film 60 is weakened.
In addition, since the aluminum-copper alloy film 60 is formed directly on a surface of the tungsten plug 59 which became rough by the step of etching the tungsten plug 59 back, <111> orientation of the aluminum-copper alloy film 60 is unlikely to be aligned.
As set forth in Japanese Unexamined Patent Publication No. 5-326511, the aluminum-copper alloy film 60 may be formed after having etched the tungsten plug 59 back and having turned the third titanium nitride film 58 into an amorphous film, in which case, however, the aluminum-copper alloy film 60 could not have a sufficient resistance to electromigration.
As a result, the wiring structure illustrated in FIG. 1 is accompanied with a problem that the upper wiring layer formed as the aluminum-copper alloy film 60 has a small resistance to electromigration, and hence, there is much dispersion in an average lifetime of wirings.
In the wiring structure illustrated in FIG. 2 as a second example of a conventional wiring structure, the second titanium film 70 is sandwiched between the second electrically insulating film 67 composed of silicon dioxide and the fourth titanium nitride film 71.
Titanium has <002> orientation, titanium nitride has <111> orientation, and aluminum-copper alloy has <111> orientation. However, it is known that the aluminum-copper alloy film 72 having <111> orientation can be obtained by forming a titanium layer and a titanium nitride layer in a multi-layered structure.
Aluminum-copper alloy predominantly contains aluminum, and could have a high resistance to electromigration, if its orientation has a peak at Al<111>. Hence, the aluminum-copper alloy film 72 as an upper wiring layer can have a sufficient resistance to electromigration.
However, the wiring structure illustrated in FIG. 2 is accompanied with a problem that a process of fabricating the wiring structure has unavoidably complexity, because the third titanium nitride film 68 has to be removed by CMP, and it would be necessary to prepare a complex and expensive apparatus for carrying out such CMP, resulting in an increase in fabrication costs. In addition, the process of fabricating the wiring structure has to unavoidably carry out additional steps to form the second titanium film 70 and the fourth titanium nitride film 71.
The wiring structure illustrated in FIG. 3 as a third example of a conventional wiring structure has the same problems as those found in the wiring structure illustrated in FIG. 2 as a second example of a conventional wiring structure.
Japanese Unexamined Patent Publication No. 11-87498 has suggested a semiconductor device including a semiconductor substrate, an electrically insulating film formed on the semiconductor substrate, a wiring layer formed on the electrically insulating film, a silicon dioxide film covering upper and side surfaces of the wiring layer therewith, and a film having a low dielectric constant and covering an upper surface of the silicon dioxide film therewith. The silicon dioxide film has a first thickness on a side surface of the wiring layer, and a second thickness on an upper surface of the wiring layer, wherein the first thickness is greater than the second thickness.
Japanese Unexamined Patent Publication No. 2000-228446 has suggested a semiconductor device including a semiconductor substrate, a lower wiring layer formed on the semiconductor substrate, an interlayer insulating film formed on the lower wiring layer, a barrier metal film composed of refractory metal and buried at a bottom of a via-hole formed throughout the interlayer insulating film and reaching the lower wiring layer, an electrically conductive film formed on the barrier metal film, and an upper wiring layer formed on the interlayer insulating film and making electrical contact with the electrically conductive film. The upper wiring layer is comprised of a first titanium film, a titanium nitride film, a second titanium film, and an aluminum or aluminum-copper alloy film.
The above-mentioned problems remain unsolved even in the semiconductor devices suggested in the above-identified Publications.